1. Field of the Invention
The present invention generally relates to an advection-type fan and an impeller thereof and, more particularly, to an advection-type fan that can guide air in and out of the fan in a horizontal direction and an impeller thereof.
2. Description of the Related Art
Conventional cooling fans are mainly categorized into two types: an axial-flow type and a blower type. The axial-flow type cooling fan has an axial air inlet and an axial air outlet opposite to the axial air inlet. Air can be drawn via the axial air inlet and then expelled via the axial air outlet. The blower type cooling fan has an axial air inlet in the axial direction and a radial air outlet in the radial direction thereof. Thus, air can be drawn via the axial air inlet and then expelled via the radial air outlet for a cooling operation.
However, the axial-flow type cooling fan must be mounted on a top of an electronic device to be cooled, such as a Central Processing Unit (CPU) of a computer. This is because the axial-flow type cooling fan can only expel air in the axial direction rather than the radial direction. Therefore, the axial height of the electronic device cannot be reduced. In addition, since the blower type cooling fan draws air via the axial air inlet (in the axial direction) and expels air via the radial air outlet (in the radial direction), the blower type cooling fan cannot be applied to electronic devices that draw air from a lateral side (from the radial direction), such as a handset or a Personal Digital Assistant (PDA).
In light of the problems, conventional advection-type fans capable of drawing and expelling air in the radial direction are currently available in the market. Such fans can be applied to electronic devices that draw air from a lateral side. However, since the modern electronic devices usually have a miniature design, the axial height of an impeller of the advection-type fan must be efficiently reduced without affecting the air-driving ability in order for the advection-type fan to be applied to the miniaturized electronic devices. The impeller of the advection-type fan is integrally formed of plastic material or integrally formed by a punching process of metal material. When the impeller is integrally formed into a predetermined shape by plastic material, the impeller may have a smaller structural strength if the impeller has a smaller thickness. Although the thin impeller may have a larger structural strength when integrally formed by a punching process of metal material, the costs are increased if a greater amount of metal material is used, and the weight is also increased when the motor drives the impeller to rotate, affecting the overall operation efficiency of the motor.
Referring to FIG. 1, Taiwan Patent No. M350746 discloses a thin rotor 8 having a thin impeller that is currently a common impeller design in the market. The rotor 8 has a metal housing 81, a shaft 82 coupled to a center of the metal housing 81, and a metal blade frame 83 extending outwards from a periphery of the metal housing 81 in a radial direction. The metal blade frame 83 is coupled with a plastic blade portion 84. In this arrangement, although the rotor 8 is thin, the rotor 8 may still have a larger structural strength, since the primary structures of the rotor 8 are the metal housing 81 and the metal blade frame 83. Further, the rotor 8 also has a lower cost, since the structure used to drive air is made of plastic (the plastic blade portion 84), allowing the rotor 8 to be manufactured in a thin form with an improved structural strength. However, the rotor 8 still has some problems stated below.
First, the rotor 8 is only suitable for use in a blower, because the air-driving faces of the plastic blade portion 84 face two opposite axial directions of the shaft 82. Although the rotor 8 may have a thin form with improved structural strength, the rotor 8 is not suitable for use in an advection-type fan.
Second, the rotor 8 has a hub 85 that blocks the airflows driven by the plastic blade portion 84. The part of the rotor 8 between the center of the metal housing 81 (where the shaft 82 is coupled) and the outer periphery of the metal blade frame 83 (where the plastic blade portion 84 is coupled) is not in a planar form. Namely, the structure of the rotor 8 where the metal housing 81 connects to the metal blade frame 83 forms the hub 85 having a protrusion form. Moreover, the top edge 841 of the plastic blade portion 84 is also not higher than the top face of the hub 85 in an axial direction. As a result, the hub 85 will block the airflows driven by the plastic blade portion 84 in a great extent when the rotor 8 is installed in an advection-type fan for driving the air in and out of the fan in the radial direction, affecting the performance of the rotor 8.
Referring to FIG. 2, another conventional advection-type fan 9 is disclosed by Taiwan Patent No. 553323 entitled “Fan Structure Having Horizontal Convection”. The conventional advection-type fan 9 includes a housing 91 and an impeller 92. The housing 91 has at least one air inlet 911 and at least one air outlet 912, with a horizontal air channel 913 formed between the at least one air inlet 911 and the at least one air outlet 912. The impeller 92 is disposed in the horizontal air channel 913 and includes a hub 921 having a plurality of blades 922 on an outer circumferential face thereof. In such an arrangement, the impeller 92 may rotate to create an air pressure difference between the at least one air inlet 911 and the at least one air outlet 912. Thus, airflows can be created between the at least one air inlet 911 and the at least one air outlet 912 for a cooling purpose.
In the above structure, since the blades 922 are formed on the outer circumferential face of the hub 921 and the top edge of each blade 922 is aligned with a top face of the hub 921, the hub 921 will block the airflows and therefore limits the airflow capacity of the advection-type fan. Thus, the cooling efficiency of the advection-type fan is significantly reduced, and turbulences and noises easily result.
In summary, the thin impeller used in a blower and the regular impeller used in a modern advection-type fan both have a common problem of larger area occupancy resulting from the hub 921, 85 taking up too much area of the air channel of the fan, reducing the airflow capacity of the fan and resulting in an unsatisfied cooling efficiency. In light of this, there exists a need to improve the advection-type fan and the impeller thereof.